#include "bits/stdc++.h"
using namespace std;
using ll = long long;
const int N = 101; //100005

char s1[N],s2[N],s[N];
int n;

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	cin >> n;
	cin >> s1;
	cin >> s2;
	for(int i=0;i<n;i++)
	{
		s[i] = min(s1[i],s2[i]);
	}
	s[n] = '\0';
	cout << s;
	return 0;
}
